We are already familiar with a closure for a container of the type indicated above from U.S. Pat. No. 3,998,354. This closure has certain disadvantages and is also not suitable for use with containers which are manufactured and filled in large numbers for the following reasons:
1. The internal width of the mouth of the container is greatly restricted by the fastener of the closure. The removal of the contents is made much more difficult, particularly where the diameter of the mouth is small. PA1 2. Although admittedly the known closure is individually formed by an injection moulding process, it does have a complicated shape. Its manufacture is consequently expensive and relatively time-consuming. From the mechanical point of view this closure is best suited for use with small openings in metal containers. The attachment to the body of the container is unreliable where the container mouth is large, with the associated risk that the closure will be several times more expensive than the actual body of the container. PA1 3. The known closure is not stackable. It is not capable of being handled in a practical manner during transport or storage. Nor is it possible to feed such closures in a practical manner to a device for closing the container. PA1 4. The known gripping device is not located in a practical manner, since it extends over the failure zone. This prevents the use of welding or similar fastening methods. PA1 5. The use of the edge of the failure zone in the lid for snapping-in in combination with compression is functionally unsatisfactory, since the edge of the failure zone will vary from one container to another. Dirt may also collect between the edge of the failure zone and the supporting flange. No reference is made in the Patent to trouble-free snapping-in. PA1 6. There are two areas in the closure where sealing may be poor, one of these being where the closure is introduced into the opening, and the other between the fastener and the lid after it has been separated from the failure zone. Poor sealing is likely to be greater at the first point than at the second. PA1 7. There is a risk of the fastener part of the closure falling from the mouth of the container as it is opened, especially in the case of large openings. PA1 8. In the case of both injection moulded and blow moulded containers, it is difficult to achieve a satisfactory fit between the container and the closure. Only special plastic materials, e.g. polyethylene, exhibit sufficient elasticity to be capable of snapping-in in the manner shown in FIG. 4 of the patent. Where the internal pressure is the same, the wall strength of the container must be high irrespective of whether it is made of metal or of a plastic material. The body of the container must always possess sufficient strength to allow the necessary reduction to take place in the dimensions of the fastener when it is attached to the container. PA1 9. An elastic plastic material such as polyethylene can easily be the cause of poor sealing, since such plastic materials change with time because they always flow a little.